The Integument

Tissues are organized in the body to form organs and systems. The integumentary system is composed of the skin (integument), nails, hairs, glands, and associated muscles and neurons (nerve cells).

The integument can be divided into two layers, the dermis (dermis = Gr. skin) and epidermis (epi = Gr. upon). The dermis is composed of connective tissue containing blood vessels, neurons, and glands. The superficial 20% of the dermis is called the papillary layer because of the bumps or papillae which characterize the surface of the region. The reticular layer accounts for the deeper four-fifths of the dermis.

Some of the dermal papillae contain Meissner's corpuscles, which are nerve endings sensitive to touch. The reticular layer contains nerve endings called Pacinian corpuscles that are sensitive to pressure.

The epidermis can be divided into four or five layers or strata (sing. - stratum). These are the stratum basale, stratum spinosum, stratum granulosum, stratum lu-cidum, and stratum corneum. Since the superficial cells of the stratum corneum are squamous, the epidermis is a stratified, squamous epithelial tissue which covers the body. The stratum lucidum occurs only in the palms and soles.

Deep to the dermis is the hypodermis (hypo = Gr. under) which attaches the skin to the underlying structures.

A notable feature of the integument is the presence of hairs (pili, sing. - pilus) located within a tube of epithelial cells called the hair follicle. The shaft of the hair is composed of packed, keratinized cells produced in the proximal end or root. The root is enlarged to form a bulb. Within the bulb is an involution, the hair papilla, through which the cells of the root are nourished. The entire root is enclosed in external and internal root sheaths which are infoldings of the epithelium.

There are two accessory structures associated with each pilus. The arrector pili muscle serves to move the hair into a vertical position. In animals this traps a layer of air and insulates the body during cold weather. The motion of the pilus against the epidermis causes the epidermis to buckle forming a "goosebump".

The sebaceous gland secretes sebum, an oily substance, onto the shaft of the hair. The sebum keeps the hair pliable and adds the waterproofing of the skin.

The deeper glands shown in Figure 6.1 are sudoriferous or sweat glands. There are two types of sudoriferous glands. Those with ducts which open directly onto the surface of the epidermis are termed merocrine (eccrine) sudoriferous glands. The glands which secrete into the hair follicle are apocrine sudoriferous glands. They can be found in the skin of the axillae (armpits), genital areas, nasal canal, and external ear canal.

Exercise 6.1

Using your textbook as a guide, label Figure 6.1. Exercise 6.2

Examine the models of the integumentary system. Be able to identify the layers of the dermis and of the epidermis, arrector pili muscle, bulb, hair papilla, pilus, root sheaths of hair follicle, sebaceous (oil) gland, and sudoriferous (sweat) glands (two kinds).

Exercise 6.3

Examine both a prepared slide of hairy skin and one of skin from the sole or palm. Identify all of the structures listed in Exercise 6.2. You may have to look at several slides to find all of the structures. The stratum basale is composed of the deepest; columnar cells of the epidermis. Cells in the stratum spinosum are spiny in some sections, while the cells of stratum granulosum contain grains of keratin (a waterproofing substance) and generally stain more darkly. Stratum comeum is the superficial layer in hairy skin. The clear cells of stratum lucidum can be seen deep to stratum comeum in non-hairy skin.

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.